<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Flex实例布局</title>
</head>
<style>
  body {
    background-color: black;
  }

  .box {
    width: 100px;
    height: 100px;
    background-color: #fff;
    display: flex;
    flex-wrap: wrap;
    align-content: space-between;
  }
  .item {
    width: 20px;
    height: 20px;
    background-color: black;
    border-radius: 50%;
  }

  .row{
    flex-basis: 100%;
    display:flex;
  }

  .row:nth-child(1){
    justify-content: space-between;
  }
  .row:nth-child(2){
    justify-content: space-between;
  }
</style>
<body>
  <div class="box">
    <div class="row">
      <span class="item"></span>
      <span class="item"></span>
      <span class="item"></span>
    </div>
    <div class="row">
      <span class="item"></span>
      <span class="item"></span>
      <span class="item"></span>
    </div>
    <!-- <div class="row">
      <span class="item"></span>
      <span class="item"></span>
    </div> -->
  </div>
</body>

<script>

</script>
</html>